A filler is ideally easy to use and produces reproducible and long-lasting results. For example, it may be desirable for the filler to be comprised of microspheres that can pass through a small needle for injection subcutaneously or intradermally, without aggregrating or agglomerating under pressure, thereby avoiding clogging of a delivery device such as a needle. Further, if microspheres are utilized, it is desirable for the microspheres to retain their distinct spherical shape without aggregating or agglomerating (hereinafter referred to as “dimensional stability”), upon manufacture, storage and physical transport. Finally, in some situations, it may desirable for these microspheres to retain their distinct spherical shape after implantation, to avoid agglomeration of the microspheres subcutaneously or interdermally, which would produce an unnatural appearance in the skin.
U.S. Pat. No. 6,716,251 describes absorbable microspheres or microparticles suspended in a gel, where the microspheres or microparticles may be polycaprolactones, polylactides, polyglycolides and their copolymers.
Although this reference suggests the use of copolymers of polycaprolactones, polylactides, and polyglycolides, preferred polymers are poly-L-lactic acid, poly-D-lactic acid, or a mixture thereof, having a molecular mass ranging from between 70,000 and 175,000 Dalton, and preferably between 120,000 and 170,000 Dalton. It is believed that the polylactide microspheres exemplified in U.S. Pat. No. 6,716,251 would have sufficient crystallinity to be dimensionally stable since poly-L-lactides and poly-D-lactides are known to be highly crystalline.
It is possible to achieve the aforementioned property, i.e., dimensional stability, for example, by utilizing amorphous copolymers of D,L-lactide or meso-lactide to make microspheres having sufficient glass transition temperature to maintain their distinct spherical shape during manufacture, storage, transportation and use. Additionally, it is desirable to utilize copolymers of D,L-lactide or meso-lactide, of specific molecular weights to make microspheres that can be absorbed in the human body within 6 to 24 months after implantation.
More specifically, it is desirable to utilize absorbable amorphous copolymers of D,L-lactide or meso-lactide, having sufficient glass transition temperature, to make microspheres that may be used, for example, in plastic surgery applications and that retain their distinct spherical shape upon manufacture, storage, and physical transportation.